Last week a malicious alteration was discovered in
event-stream, a widely
downloaded npm package. Full details are in the
npm team's write up, but the tl;dr is that a bad
actor was added as a maintainer of
event-stream and inserted
malware into a new release. The malware was discovered three months later.
It's not the first time an attacker has gained access to a popular npm package - in July a similar attack targeted ESLint users.
How do we solve this one? We think there are four broad themes:
- Make it harder for attackers to hijack packages
- Make it easier for maintainers to detect hijacks
- Make it easier for users to detect hijacked packages
- Make the response to known insecure packages faster
Dependabot can help with some of the above. Other issues need to be tackled by npm and other language registries (many of which are open source and need your help). Still others need cultural changes.
event-stream attacks show two different ways attackers
can get malicious code into a release:
- In the
eslint-scopecase a maintainer's credentials were compromised after they had reused their password on other sites
- In the
event-streamcase a maintainer was tricked into granting npm privileges to the attacker, who posed as a new maintainer
Additionally, an attacker doesn't need to get release access on npm if they can convince a maintainer to merge a PR that pulls in the malicious code. There's a (fictional) account of that in this blog post.
The compromised credentials case is the easiest to prevent. Two factor authentication makes a big difference here. Ideally, we believe it should be compulsory when publishing releases of packages with over a certain threshold of downloads each week.
Preventing social engineering attacks is harder. Since the
there's been good (and bad!) discussion about how to make open source
maintenance more sustainable. Initiatives like Jazzband surely have
a role to play, alongside the various organisations trying to make open source
financially sustainable. We don't have a clear recommendation here.
- All registries should implement some form of two-factor authentication, and require it for popular packages
The first line of defence against a package hijack is the package maintainers. If they're engaged, and for most popular projects they are, they're best placed to both spot and shut down the hijack.
In response to the
eslint-scope attack the npm team implemented email alerts
to all maintainers whenever a new version of a package is published. That's
hugely valuable - it means that if a maintainer's credentials are compromised
they will discover it as soon as a new release is cut. It's also an incredibly
simple fix to implement, and we'd encourage all registries to do so. You can
help - many are open source.
Email alerts didn't help with
event-stream attack, however, because the only
maintainer was now the attacker. In that case only users can detect the hijack.
- All registries should notify maintainers each time a release is cut. If a maintainer's credentials are compromised this ensures they hear about it
The most worrying thing about the
event-stream attack is that it took 3 months
to detect, despite 2 million weekly downloads.
Detection was slow because most users have no direct interaction with
event-stream. Like many JS dependencies it is almost always pulled in as a
transitive dependency.1 In this case the attack took further
advantage of transitive dependencies being inscrutable - the
commit responsible for the attack introduces a new,
malicious dependency to
Dependabot can help a little here, by making it easier for users that do directly import a dependency to review changes to it. We already include changelogs, release notes and commit diffs in our PRs, but starting today we're experimenting with also highlighting when a version has been released by a new maintainer. We suggest users apply additional scrutiny when upgrading to such releases, and hope it will help spot future hijacks.
There's more to be done here, however. The commit diffs that Dependabot links to on the source repo, for example, are not guaranteed to match the diff on npm, because npm doesn't publish the git commit SHA that was used to build the package (or, indeed, require one at all). Transitive dependencies remain a soft target as fewer users apply scrutiny to them when updating.
We'd like to do even more here, and are continuing to think on ways we can help.
- Dependabot is experimenting with including details of the new maintainer in our pull requests if they have changed
- To help users review dependency updates for malicious changes, npm and GitHub should make it easy to check the check the integrity of an npm package against a git tag
When a hijacked dependency versions is found the required response is similar to any other dependency insecurity:
- A patched version (normally) needs to be released
- All users of the dependency need to be informed as quickly as possible
- All users should almost always needs to upgrade to the patched version
This is one area where we already have great tools to help us. GitHub's Security Alerts, the Node Security Working Group, and npm's own security database all provide data to inform users of new vulnerabilities.
Dependabot consumes that security data and automatically creates pull requests to upgrade our users to patched versions the moment a vulnerability is announced. It provides details of the vulnerability being fixed in the PR description, alongside the diff, release notes and any changelog entry.
- Use Dependabot to automatically receive fix PRs for any insecure dependencies (transitive or direct). Other services like [Snyk][:snyk] also exist for some languages, but we're biased on this one 🤖
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